The present invention relates generally to fuel injectors for gas turbine engines of aircraft, and more particularly to fuel swirlers for such fuel injectors.
Fuel injectors for gas turbine engines on an aircraft direct fuel from a manifold to a combustion chamber. The fuel injector typically has an inlet fitting connected to the manifold for receiving the fuel, a fuel spray nozzle located within the combustion chamber of the engine for atomizing (dispensing) the fuel, and a housing stem extending between and supporting the fuel nozzle with respect to the fitting. Appropriate check valves and/or flow dividers can be disposed within the fuel nozzle to control the flow of fuel through the nozzle. The fuel injector is typically heatshielded to protect the injector from the high operating temperatures within the engine casing. The fuel injector has an attachment flange which enables multiple injectors to be attached to the combustor casing of the engine in a spaced-apart manner around the combustor to dispense fuel in a generally cylindrical pattern.
Fuel tube(s) are provided through the housing stem, and typically direct fuel received in the fitting into an annulus surrounding the upstream end of a fuel swirler in the nozzle. The fuel is then directed downstream along the fuel swirler in an annular flow, or in a series of discrete passages, to discharge orifices. At the downstream end of the swirler, the passages are angled, or swirler vanes are provided, to impart a swirling component of motion to the fuel. The swirling fuel is applied against an annular prefilmer outwardly surrounding the fuel swirler, and then impacted by inner and outer swirling air flows to provide an atomized fuel spray. The swirling, atomized spray is ignited downstream of the nozzle in the combustor. Examples of such nozzles are shown in U.S. Pat. Nos. 3,980,233; 5,761,907; and 6,076,356.
While the nozzle design described above has been used for many years and provides a satisfactory fuel spray, one drawback of such a design is that, at low fuel flow rates and pressures typical of start up conditions, the fuel entering the annulus tends to be directed by pressure and gravity to the lower (6 o""clock) portion of the annulus. A greater amount of fuel is then directed through the passages at the lower portion to the discharge orifices. The resulting spray tends to have streaks of fuel, which decreases the efficiency of combustion and the stability of the flame. At high power conditions, the 6 o""clock pocket tends to accumulate some of the fuel due to the presence of a recirculation zone. The residence time of the fuel is increased significantly, thereby increasing the propensity for carbon formation. In low fuel velocity regions, local heat transfer coefficients are also reduced resulting in increased wetted wall temperatures, which can lead to coking internally of the fuel passages.
U.S. Pat. No. 5,799,872 shows and describes a main injector having a pair of inlet chambers along a fuel swirler, where each inlet chamber receives fuel from a separate fuel conduit, and directs the fuel along one or more curved fuel passages to downstream discharge orifices. The discharge orifices associated with each chamber appear to be spaced about ninety degrees apart from each other, or otherwise around only a portion of the nozzle, as the orifices from the other fuel circuit are located on the opposite side of the nozzle tip. A pilot injector is also shown, where a single fuel conduit feeds a single inlet chamber leading to plural fuel passages. The main injector includes air passages in certain of the fuel passages which interconnect the fuel passages with the inner air channel to create back pressure for fuel purging purposes. It is believed such air passages would decrease the uniformity of the spray, and hence decrease the efficiency of combustion. Also, such passages could allow fuel to enter the inner air channel, which could lead to coking internally of the swirler. The fuel passages along the fuel swirler (at least for the main injector) are also curved, which can be difficult to machine. Still further, the inlet chambers appear to have small dimensions, which could restrict fuel flow into the passages, and hence increase the pressure drop across the nozzle.
Thus it is believed there is a demand in the industry for a further improved fuel injector for gas turbine engines, and particularly for a fuel swirler for such an injector, which provides a uniform spray for efficient combustion and stability of the flame; minimizes the pressure drop across the swirler; is simple and low-cost to manufacture; and prevents coking internally of the nozzle.
The present invention provides a novel and unique fuel injector for a gas turbine engine of an aircraft, and more particularly, a novel and unique fuel swirler for the fuel injector. The fuel swirler provides uniform spray for efficient combustion and stability of the flame; minimizes the pressure drop across the fuel swirler; is simple and low-cost to manufacture; and prevents coking internally of the nozzle.
According to the principles of the present invention, the fuel injector has an inlet fitting for receiving fuel, a fuel nozzle for dispensing fuel, and a housing stem fluidly interconnecting the fuel nozzle and the fitting. The fuel injector can be easily assembled with the engine combustor by a flange extending outwardly from the housing stem, and easily disassembled for inspection or replacement.
The fuel nozzle includes a fuel swirler, which directs fuel from a fuel conduit in the housing stem to discharge openings at the downstream end of the swirler. The fuel swirler includes a gallery or plenum for receiving the fuel from the fuel conduit. A plurality of fuel passages are provided to direct fuel from the plenum downstream along the fuel swirler. Each passage opens at the upstream end to the plenum, and terminates at its downstream end in a discharge orifice. The downstream end of the passages are angled such that a swirl component of motion is imparted to the fuel exiting the discharge orifices. The swirling fuel is then applied to a prefilmer, which outwardly surrounds the fuel swirler.
The passages in the fuel swirler are arranged such that the discharge orifices surround the entire nozzle for the even distribution of fuel. The plenum and passages are also dimensioned to receive and distribute the fuel for uniform spray patternization and low pressure drop. The uniform spray patternization and low pressure drop provide improved combustion and flame stability. The fuel residence time in the nozzle is also minimized, which prevents coking.
The present invention thereby provides an improved fuel injector for gas turbine engines, and particularly an improved fuel swirler for such an injector, which provides a uniform spray for efficient combustion and stability of the flame; minimizes the pressure drop across the swirler; is simple and low-cost to manufacture; and prevents coking internally of the nozzle.
Other features and advantages of the present invention will become further apparent upon reviewing the following specification and attached drawings.